OFDM is a modulation technique that effectively partitions the overall system bandwidth into a number of (N) orthogonal subbands. Each subband is associated with a respective subcarrier that may be modulated with data. The subbands are also commonly referred to as tones, subcarriers, bins, and frequency channels.
OFDM is widely used in various communication systems. For example, an orthogonal frequency division multiple access (OFDMA) system utilizes OFDM and can support multiple users. The N subbands may be used for data and pilot transmission in various manners, depending on the system design. For example, the OFDMA system may partition the N subbands into multiple disjoint groups of subbands and allocate each subband group to a different user. Multiple users can then be supported simultaneously via their assigned subband groups.
In many instances, it is only necessary to demodulate a subset of the N subbands in an OFDM-based system. A straightforward method to process a subset of the N subbands is to perform an N-point fast Fourier transform (FFT) on time-domain samples to obtain frequency-domain symbols for all N subbands. The symbols for the subbands of interest are then extracted and processed, and the symbols for all other subbands are discarded. This straightforward method requires memory storage proportional to the N subbands and further requires computation for all N subbands, even if only a small subset of the N subbands is used for data transmission.
There is therefore a need in the art for techniques to more efficiently perform demodulation in an OFDM-based system when only a subset of the N subbands is used for data transmission.